Medical practitioners have found it useful to use robotic systems to assist in the performance of surgical procedures. Such robotic systems may include a force controlled robot having a moveable arm and an end effector at the end of the arm. Typically, a surgical tool is attached to the end effector. The tool is designed to be applied to a surgical site. Generally, a controller regulates movement of the arm to position the tool with a high degree of accuracy at the surgical site. Optimum control of the force controlled robot is achieved by directly sensing forces applied by a user at a location where the user interacts with the robot. This is typically at the end effector/robot arm interface or part of the end effector itself.
A component of many robotic systems is a force/torque sensor. The force/torque sensor is typically attached between the free end of the arm and the tool. The force/torque sensor monitors forces and torques that are applied to the tool. These may be forces and torques that are applied to the tool as a consequence of the tool pressing against tissue. These also may be forces and torques a user applies in order to set a position and/or orientation of the tool. Signals output by the force/torque sensor are received by the controller. The controller uses these signals to determine a target position for the tool. Based on the determined target position, the controller actuates the arm in order to advance the arm so that the tool is moved to the target position.
In order to ensure all forces and torques applied to the tool are measured, it is common practice to provide a six component force/torque sensor. This type of force/torque sensor measures forces applied to the tool along three axes and torques applied to the tool around the three axes.
One type of six component force/torque sensor is also known as a force/torque transducer. A typical force/torque transducer includes a pair of sensor members, one for attaching to the robot arm and one for attaching to the end effector. A plurality of beams is flexibly mounted between the sensor members and one or more strain gauges are associated with each beam. Each strain gauge generates an electrical signal proportional to a flexure of the beam with which the strain gauge is associated. The output signals from the strain gauges are input variables into an algorithm that yields the measured forces and torques.
One disadvantage of the above force controlled robot is that the force/torque sensor is subjected to all other forces imparted to the tool in addition to the forces presented by the user and these other forces may be in a range that is capable of exceeding the operating range of the force/torque sensor or even high enough to damage the force/torque sensor. This is especially true when the use-case of the force controlled robot is to be a manual positioner for a high impact procedure such as impacting an acetabular cup in a total hip arthroplasty. In this application, the user guides the robot into the correct position to hold the impactor using traditional force control and then manually strikes the tool with a hammer, subjecting the force/torque sensor to the impact forces. Therefore, there is a need in the art to provide a force/torque sensor for a force controlled robot that isolates the force/torque sensor such that the impacting forces are not imparted to the force/torque sensor.